Add EmitterStyle, which will allow sequence or map style (i.e., flow or block) to be preserved between parsing and emitting

Add yaml-cpp-config.cmake and yaml-cpp-config-version.cmake files for importing yaml-cpp into external projects (through find_package).

Fix clang compiler settings, and properly set up warnings so they don't interfere with gtest and gmock

See, e.g., http://stackoverflow.com/questions/4738768/printing-double-without-losing-precision.